Cardiac catheterization is carried out by memorizing a designationof a contact state between an electrode of the probe and theheart wall as one of an in-contact state and an out-of-contact state,and making a series of determinations of an impedance phase angleof an electrical current passing through the electrode and anotherelectrode, identifying maximum and minimum phase angles in the series,and defining a binary classifier adaptively as midway betweenthe extremes. A test value is compared to the classifier as adjusted bya hysteresis factor, and a change in the contact state is reported whenthe test value exceeds or falls below the adjusted classifier.
